Glass substrate for high-frequency device and circuit board for high-frequency device

ABSTRACT

The present invention relates to a glass substrate for a high-frequency device, which includes SiO 2  as a main component, the glass substrate having a total content of alkali metal oxides in the range of 0.001-5% in terms of mole percent on the basis of oxides, the alkali metal oxides having a molar ratio represented by Na 2 O/(Na 2 O+K 2 O) in the range of 0.01-0.99, and the glass substrate having a total content of Al 2 O 3  and B 2 O 3  in the range of 1-40% in terms of mole percent on the basis of oxides and having a molar ratio represented by Al 2 O 3 /(Al 2 O 3 +B 2 O 3 ) in the range of 0-0.45, in which at least one main surface of the glass substrate has a surface roughness of 1.5 nm or less in terms of arithmetic average roughness Ra, and the glass substrate has a dielectric dissipation factor at 35 GHz of 0.007 or less.

TECHNICAL FIELD

The present invention relates to a glass substrate for a high-frequencydevice and a circuit board for a high-frequency device.

BACKGROUND ART

In the field of electronic devices such as communication appliances suchas cell phones, smartphones, personal digital assistants and Wi-Fiappliances, surface acoustic wave (SAW) devices, radar components, andantenna components, use of higher signal frequencies is being advancedin order to increase the communication capacity, heighten thecommunication speed, etc. Circuit boards for use in electronicappliances for such high-frequency applications generally employinsulating substrates such as resin substrates, ceramic substrates, andglass substrates. The insulating substrates for use in high-frequencydevices are required to reduce transmission losses based on dielectricloss, conductor loss, etc. in order to ensure the quality, intensity,and other properties of high-frequency signals.

Among such insulating substrates, resin substrates have low rigidity dueto the nature thereof. Because of this, it is difficult to apply resinsubstrates in the case where rigidity (strength) is required for thesemiconductor package products. Ceramic substrates have a drawback inthat it is difficult to heighten the surface smoothness thereof and thisis prone to result in an increased conductor loss due to the conductorformed on the substrate surface. Meanwhile, glass substrates arecharacterized by having high rigidity to make size and thicknessreductions, etc. of packages easy, and by having excellent surfacesmoothness and being easily produced as larger-size substrates.

BACKGROUND ART DOCUMENT Patent Document

Patent Document 1: JP-A-2013-077769

Patent Document 2: JP-A-2004-244271

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

However, conventional alkali-free glass substrates, although effectivein reducing dielectric loss and transmission loss based thereon atfrequencies up to about 20 GHz, have limitations in reducing thedielectric loss in a high-frequency range beyond, for example, 30 GHz.It is hence difficult for circuit boards employing conventionalalkali-free glass substrates to maintain the quality, intensity, andother properties of high-frequency signals having a frequency exceeding30 GHz. Meanwhile, quartz glass substrates can retain a low dielectricloss even in the range of frequencies exceeding 30 GHz. However, thequartz glass substrates have a drawback in that the thermal expansioncoefficient thereof is so low that there is too large a difference inthermal expansion coefficient between the quartz glass substrate andother members in configuring an electronic device. This is a factorwhich lowers the suitability for practical use of the electronic device.

An object of the present invention is to provide: a glass substrate fora high-frequency device, the glass substrate being capable of reducingthe dielectric loss of high-frequency signals and of providing practicalelectronic devices; and a circuit board for a high-frequency device, thecircuit board employing the glass substrate and being capable ofreducing the transmission loss of high-frequency signals.

Means for Solving the Problems

A glass substrate for a high-frequency device according to a firstembodiment of the present invention is a glass substrate for ahigh-frequency device, which includes SiO₂ as a main component, theglass substrate having a total content of alkali metal oxides in therange of 0.001-5% in terms of mole percent on the basis of oxides, thealkali metal oxides having a molar ratio represented by Na₂O/(Na₂O+K₂O)in the range of 0.01-0.99, and the glass substrate having a totalcontent of Al₂O₃ and B₂O₃ in the range of 1-40% in terms of mole percenton the basis of oxides and having a molar ratio represented byAl₂O₃/(Al₂O₃+B₂O₃) in the range of 0-0.45, in which at least one mainsurface of the glass substrate has a surface roughness of 1.5 nm or lessin terms of arithmetic average roughness Ra, and the glass substrate hasa dielectric dissipation factor at 35 GHz of 0.007 or less.

A glass substrate for a high-frequency device according to a secondembodiment of the present invention is a glass substrate for ahigh-frequency device, which includes SiO₂ as a main component, theglass substrate having a total content of alkali metal oxides in therange of 0.001-5% in terms of mole percent on the basis of oxides, thealkali metal oxides having a molar ratio represented by Na₂O/(Na₂O+K₂O)in the range of 0.01-0.99, and the glass substrate having a totalcontent of alkaline earth metal oxides in the range of 0.1-13% in termsof mole percent on the basis of oxides, in which at least one mainsurface of the glass substrate has a surface roughness of 1.5 nm or lessin terms of arithmetic average roughness Ra, and the glass substrate hasa dielectric dissipation factor at 35 GHz of 0.007 or less.

A circuit board for a high-frequency device according to a thirdembodiment of the present invention is a circuit board for ahigh-frequency device, including: the glass substrate according to thefirst embodiment or the second embodiment of the present invention; anda wiring layer formed on the main surface of the glass substrate, inwhich the circuit board has a transmission loss at 35 GHz of 1 dB/cm orless.

Advantage of the Invention

According to the glass substrate for a high-frequency device of thepresent invention, it is possible to reduce the dielectric loss ofhigh-frequency signals. According to the circuit board employing thisglass substrate, the transmission loss of high-frequency signals can bereduced and it is possible to provide a practical high-frequency device,e.g., electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating the configuration of acircuit board according to an embodiment.

FIG. 2 is a chart which shows relationships between signal frequency andtransmission loss in the circuit boards according to Examples 1 to 6.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are explained. Each numerical rangegiven with “-” includes the numerical values that precede and succeedthe “-”, as the lower limit and the upper limit, respectively. Thecontent of each component in a glass substrate is given in terms of molepercent (mol %) on the basis of oxides unless otherwise indicated. Inthis description, the term “high-frequency” means frequencies of 10 GHzor higher, preferably higher than 30 GHz, more preferably 35 GHz orhigher.

FIG. 1 illustrates a circuit board for a high-frequency device accordingto an embodiment of the present invention. The circuit board 1illustrated in FIG. 1 includes a glass substrate 2 having insulatingproperties, a first wiring layer 3 formed on a first main surface 2 a ofthe glass substrate 2, and a second wiring layer 4 formed on a secondmain surface 2 b of the glass substrate 2. The first and second wiringlayers 3 and 4 form microstrip lines as an example of transmissionlines. The first wiring layer 3 constitutes signal wiring and the secondwiring layer 4 constitutes ground wiring. However, the structures of thefirst and second wiring layers 3 and 4 are not limited to these, and thewiring layers may have been formed only on one main surface of the glasssubstrate 2.

The first and second wiring layers 3 and 4 are layers formed by aconductor and have a thickness of usually about 0.1 μm to 50 μm. Theconductor which constitutes the first and second wiring layers 3 and 4is not particularly limited, and use is made, for example, of metalssuch as copper, gold, silver, aluminum, titanium, chromium, molybdenum,tungsten, platinum, and nickel, alloys or metal compounds containing atleast one of these metals, etc. The structures of the first and secondwiring layers 3 and 4 are not limited to a single-layer structure, andthe wiring layers 3 and 4 may have a structure including a plurality oflayers, such as a multilayer structure including a titanium layer and acopper layer. Methods for forming the first and second wiring layers 3and 4 are not particularly limited. For example, various known formationmethods can be applied, such as a printing method in which a conductorpaste is used, dipping, plating, vapor deposition, and sputtering.

The glass substrate 2 includes a glass substrate for a high-frequencydevice according to an embodiment of the present invention and has theproperty of having a dielectric dissipation factor (tan δ) at 35 GHz of0.007 or less. The glass substrate 2 preferably has a relativepermittivity at 35 GHz of 10 or less. Since the glass substrate 2 has adielectric dissipation factor at 35 GHz of 0.007 or less, this glasssubstrate 2 can be reduced in dielectric loss in the range offrequencies exceeding 30 GHz. Also by regulating the relativepermittivity at 35 GHz of the glass substrate 2 to 10 or less, thedielectric loss in a high-frequency range can be reduced. The dielectricdissipation factor at 35 GHz of the glass substrate 2 is more preferably0.005 or less, even more preferably 0.003 or less. The relativepermittivity of the glass substrate 2 is more preferably 7 or less, evenmore preferably 6 or less, especially preferably 5 or less.

The main surfaces 2 a and 2 b of the glass substrate 2, on which thefirst and second wiring layers 3 and 4 are to be formed, have a surfaceroughness of 1.5 nm or less in terms of arithmetic average roughness Ra.Since the main surfaces 2 a and 2 b of the glass substrate 2, on whichthe first and second wiring layers 3 and 4 are to be formed, have anarithmetic average roughness Ra of 1.5 nm or less, the first and secondwiring layers 3 and 4 can be reduced in skin resistance even when a skineffect has occurred in the first and second wiring layers 3 and 4 in ahigh-frequency range beyond 30 GHz, thereby attaining a reduction inconductor loss. The arithmetic average roughness Ra of the main surfaces2 a and 2 b of the glass substrate 2 is more preferably 1.0 nm or less,even more preferably 0.5 nm or less. The term “main surface of the glasssubstrate 2” means a surface on which a wiring layer is to be formed. Inthe case where the wiring layers are formed on one main surface, it isonly required that the one main surface should have an arithmeticaverage roughness Ra of 1.5 nm or less. The term “surface roughness Ra”in this description means a value obtained in accordance with JIS B0601(year 2001).

The surface roughness of the main surfaces 2 a and 2 b of the glasssubstrate 2 can be attained by subjecting the surfaces of the glasssubstrate 2 to a polishing treatment or the like according to need. Thesurfaces of the glass substrate 2 can be polished, for example, by:mechanical polishing with an abrasive including cerium oxide, colloidalsilica, or the like as a main component and with a polishing pad;chemical-mechanical polishing in which a polishing slurry, whichincludes an abrasive and an acidic or alkaline liquid as a dispersionmedium, and a polishing pad are used; or chemical polishing in which anacidic liquid or an alkaline liquid is used as an etchant. Thesepolishing treatments are used in accordance with the surface roughnessof the glass plate to be used as a material for the glass substrate 2.For example, preliminary polishing and finish polishing may be conductedin combination. It is preferable that the edge surfaces of the glasssubstrate 2 have been chamfered in order to prevent the glass substrate2, when being processed, from suffering breakage, cracking, or chippingwhich occurs from an edge surface. The chamfering may be any ofC-chamfering, R-chamfering, light-chamfering, etc.

Due to the use of the glass substrate 2 having such properties, thecircuit board 1 can have a reduced transmission loss at 35 GHz,specifically, 1 dB/cm or less. Consequently, the quality, intensity, andother properties of high-frequency signals, in particular,high-frequency signals having a frequency exceeding 30 GHz and evenhigh-frequency signals of 35 GHz or higher, are maintained. Thus, aglass substrate 2 and a circuit board 1 that are suitable forhigh-frequency devices in which such high-frequency signals areprocessed can be provided. Namely, the characteristics and quality ofhigh-frequency devices in which such high-frequency signals areprocessed can be improved. The transmission loss at 35 GHz of thecircuit board 1 is more preferably 0.5 dB/cm or less.

A glass substrate 2 having the above-described dielectric propertiesincluding dielectric dissipation factor can be attained by forming aglass substrate including SiO₂ as a main component and as anetwork-forming substance so that the glass substrate satisfiesrequirements (1) and (2), or requirements (1) and (3), or requirements(1), (2), and (3), which are shown below. The glass substrate 2 isformed by melting and hardening a raw-material composition. Althoughmethods for producing the glass substrate 2 are not particularlylimited, use can be made, for example, of a method in which ageneral-purpose molten glass is formed into a sheet having a giventhickness by the float process and the sheet is annealed and then cutinto a desired shape to obtain a plate glass.

The term “glass” in this description means a solid which is amorphous,as defined, and shows glass transition. The term does not mean acrystallized glass, which is a mixture of a glass and crystals, or asintered glass which contains a crystalline filler. That a glass isentirely amorphous can be ascertained by examining the glass by X-raydiffractometry and ascertaining the absence of any distinctivediffraction peak.

In this description, the expression “including SiO₂ as a main component”means that the content of SiO₂, in component proportion in terms of molepercent on the basis of oxides, is the highest.

Requirement (1): the glass substrate 2 has a total content of alkalimetal oxides in the range of 0.001-5%, the alkali metal oxides having amolar ratio represented by Na₂O/(Na₂O+K₂O) in the range of 0.01-0.99.

Requirement (2): the glass substrate (2) has a total content of Al₂O₃and B₂O₃ in the range of 1-40% and has a molar ratio represented byAl₂O₃/(Al₂O₃+B₂O₃) in the range of 0-0.45.

Requirement (3): the glass substrate 2 has a total content of alkalineearth metal oxides in the range of 0.1-13%.

With respect to requirement (1), the low-dielectric-loss characteristicsof the glass substrate 2, which includes SiO₂ as a main component, canbe enhanced by regulating the content of alkali metal oxides in theglass substrate 2 to 5% or less. Meanwhile, by regulating the content ofalkali metal oxides therein to 0.001% or higher, not only practicalglass meltability and practical efficiency of producing the glasssubstrate 2 are obtained without necessitating excess purification ofraw materials but also the thermal expansion coefficient of the glasssubstrate 2 can be regulated. Examples of the alkali metal oxides whichcan be contained in the glass substrate 2 include Li₂O, Na₂O, K₂O, Rb₂O,and Cs₂O, but Na₂O and K₂O are especially important. It is hencepreferable that the total content of Na₂O and K₂O is in the range of0.001-5%. The content of alkali metal oxides is desirably 3% or less,preferably 1% or less, even more preferably 0.2% or less, in particular0.1% or less, especially preferably 0.05% or less. The content of alkalimetal oxides is more preferably 0.002% or higher, even more preferably0.003% or higher, especially preferably 0.005% or higher.

Furthermore, by causing Na₂O and K₂O to coexist in a vitreous substanceincluding SiO₂ as a main component, in other words, by regulating themolar ratio represented by Na₂O/(Na₂O+K₂O) to a value in the range of0.01-0.99, the alkali components are inhibited from moving and, hence,the low-dielectric-loss characteristics of the glass substrate 2 can beenhanced. The molar ratio represented by Na₂O/(Na₂O+K₂O) is morepreferably 0.98 or less, even more preferably 0.95 or less, especiallypreferably 0.9 or less. The molar ratio represented by Na₂O/(Na₂O+K₂O)is more preferably 0.02 or higher, even more preferably 0.05 or higher,especially preferably 0.1 or higher.

The glass substrate 2 is made to satisfy requirement (2), concerning thecontent and proportion of Al₂O₃ and B₂O₃, or requirement (3), concerningthe content of alkaline earth metal oxides, or to satisfy bothrequirement (2) and requirement (3), in addition to the requirement (1),which specifies the content of alkali metal oxides and a proportion ofalkali metal oxides. Thus, the glass substrate 2 can be made to have adielectric dissipation factor at 35 GHz of 0.007 or less. With respectto requirement (2), Al₂O₃ is not essential. However, Al₂O₃ is acomponent which is effective in improving the weatherability, inhibitingthe glass from separating into phases, lowering the thermal expansioncoefficient, etc., and the content thereof is preferably in the range of0-15%. B₂O₃ is a component which is effective in improving glassmeltability, lowering the devitrification temperature, etc., and thecontent thereof is preferably in the range of 9-30%.

With respect to requirement (2), in cases when the molar ratiorepresented by Al₂O₃/(Al₂O₃+B₂O₃) is 0.45 or less, thelow-dielectric-loss characteristics of the glass substrate 2 can beheightened. The molar ratio represented by Al₂O₃/(Al₂O₃+B₂O₃) may be 0.The molar ratio represented by Al₂O₃/(Al₂O₃+B₂O₃) is more preferably 0.4or less, even more preferably 0.3 or less. The molar ratio representedby Al₂O₃/(Al₂O₃+B₂O₃) is preferably 0.01 or higher, more preferably 0.05or higher.

In cases when the total content of Al₂O₃ and B₂O₃ (including the casewhere the content of Al₂O₃ is 0) is 1% or higher, the glass can haveenhanced meltability, etc. The total content of Al₂O₃ and B₂O₃ is morepreferably 3% or higher, even more preferably 5% or higher, especiallypreferably 7% or higher. In cases when the total content of Al₂O₃ andB₂O₃ (including the case where the content of Al₂O₃ is 0) is 40% orless, the low-dielectric-loss characteristics of the glass substrate 2can be enhanced while maintaining glass meltability, etc. The totalcontent of Al₂O₃ and B₂O₃ is more preferably 37% or less, even morepreferably 35% or less, especially preferably 33% or less.

In cases when the content of Al₂O₃ is 15% or less, glass meltability andother properties can be rendered satisfactory. The content of Al₂O₃ ismore preferably 14% or less. The content of Al₂O₃ is more preferably0.5% or higher. In cases when the content of B₂O₃ is 30% or less, theglass substrate can have satisfactory acid resistance and a satisfactorystrain point. The content of B₂O₃ is more preferably 28% or less, evenmore preferably 26% or less, especially preferably 24% or less, mostpreferably 23% or less. Meanwhile, in cases when the content of B₂O₃ is9% or higher, the meltability can be improved. The content of B₂O₃ ismore preferably 13% or higher, even more preferably 16% or higher.

With respect to requirement (3), examples of the alkaline earth metaloxides include MgO, CaO, SrO, and BaO. These oxides each function as acomponent which enhances glass meltability. In cases when the totalcontent of such alkaline earth metal oxides is 13% or less, the glasssubstrate 2 can have enhanced low-dielectric-loss characteristics. Thetotal content of alkaline earth metal oxides is more preferably 11% orless, even more preferably 10% or less, especially preferably 8% orless, most preferably 6% or less. Meanwhile, in cases when the totalcontent of alkaline earth metal oxides is 0.1% or higher, satisfactoryglass meltability can be maintained. The total content of alkaline earthmetal oxides is more preferably 3% or higher, even more preferably 5% orhigher.

MgO, although not essential, is a component which heightens the Young'smodulus without increasing the specific gravity. Namely, MgO is acomponent capable of heightening the specific modulus, therebymitigating the problem of deflection and improving the fracturetoughness to enhance the glass strength. MgO is also a component whichimproves meltability. The content of MgO, which is not an essentialcomponent, is preferably 0.1% or higher, more preferably 1% or higher,even more preferably 3% or higher. In cases when the content of MgO is0.1% or higher, the effects of the inclusion of MgO can be sufficientlyobtained and the thermal expansion coefficient can be inhibited frombecoming too low. The content of MgO is preferably 13% or less, morepreferably 11% or less, even more preferably 9% or less. In cases whenthe content of MgO is 13% or less, the devitrification temperature canbe inhibited from rising.

CaO is a component which has the feature of being next to MgO, among thealkaline earth metal oxides, in heightening the specific modulus and ofnot excessively lowering the strain point and which improves meltabilitylike MgO. CaO further has the feature of being less apt to heighten thedevitrification temperature as compared with MgO. The content of CaO,which is not an essential component, is preferably 0.1% or higher, morepreferably 1% or higher, even more preferably 3% or higher. In caseswhen the content of CaO is 0.1% or higher, the effects of the inclusionof CaO can be sufficiently obtained. The content of CaO is preferably13% or less, more preferably 10% or less, even more preferably 8% orless. In cases when the content of CaO is 13% or less, the glass isprevented from having too high an average thermal expansion coefficientand is inhibited from increasing in devitrification temperature, therebypreventing devitrification during glass production.

SrO is a component which improves meltability without heightening thedevitrification temperature of the glass. The content of SrO, which isnot an essential component, is desirably 0.1% or higher, preferably 0.5%or higher, more preferably 1.0% or higher, even more preferably 1.5% orhigher, especially preferably 2% or higher. In cases when the content ofSrO is 0.1% or higher, the effect of the inclusion of SrO can besufficiently obtained. The content of SrO is preferably 13% or less,more preferably 10% or less, even more preferably 7% or less, especiallypreferably 5% or less. In cases when the content of SrO is 13% or less,the glass can be prevented from having too high a specific gravity andbe inhibited from having too high an average thermal expansioncoefficient.

BaO, although not essential, is a component which improves meltabilitywithout heightening the devitrification temperature of the glass.However, in case where BaO is contained in too large an amount, theglass tends to have too high a specific gravity, a reduced Young'smodulus, an increased relative permittivity, and too high an averagethermal expansion coefficient. Because of this, the content of BaO isdesirably 10% or less, preferably 8% or less, more preferably 5% orless, even more preferably 3% or less. It is especially preferable thatthe glass substrate contains substantially no BaO.

In this description, the wording “containing substantially no . . . ”means that the ingredient is not contained except for that which hascome into the glass as an unavoidable impurity from raw materials, etc.Namely, that wording means that the ingredient is not incorporated onpurpose. In the present invention, the expression “the glass containssubstantially no BaO” means that the content thereof is, for example,0.3% or less.

As described above, in cases when requirement (2) or (3) is satisfiedbesides requirement (1), the glass substrate 2 can have a dielectricdissipation factor at 35 GHz of 0.007 or less and can have a reduceddielectric loss. From the standpoint of further enhancing thelow-dielectric-loss characteristics of the glass substrate 2, it is morepreferable that the glass substrate 2 satisfies all of requirement (1),requirement (2), and requirement (3).

The content of SiO₂, among the constituent components of the glasssubstrate 2, that is a main component and serves as a network-formingsubstance is preferably in the range of 40-75%. In cases when thecontent of SiO₂ is 40% or higher, satisfactory glass-forming ability andsatisfactory weatherability can be obtained and devitrification can beinhibited. The content of SiO₂ is more preferably 45% or higher, evenmore preferably 50% or higher, especially preferably 55% or higher.Meanwhile, in cases when the content of SiO₂ is 75% or less,satisfactory glass meltability can be attained. The content of SiO₂ ismore preferably 74% or less, even more preferably 73% or less,especially preferably 72% or less.

The glass substrate 2 may contain Fe₂O₃, TiO₂, ZrO₂, ZnO, Ta₂O₅, WO₃,Y₂O₃, La₂O₃, etc. as optional components, besides the componentsdescribed above. Fe₂O₃ is a component for controlling thelight-absorbing performance of the glass substrate 2, such as, forexample, infrared-absorbing performance or ultraviolet-absorbingperformance. The glass substrate 2 can contain Fe, in terms of Fe₂O₃, inan amount of up to 0.012% according to need. In cases when that contentof Fe is 0.012% or less, the glass substrate 2 can retain thelow-dielectric-loss characteristics and ultraviolet transmittance. Fromthe standpoint of improving the ultraviolet transmittance, the contentof Fe is more preferably 0.01% or less, even more preferably 0.005% orless. By heightening the ultraviolet transmittance of the glasssubstrate 2, it is rendered possible to use an ultraviolet-curingmaterial in, for example, stacking steps in high-frequency deviceproduction steps, thereby heightening the efficiency of producinghigh-frequency devices.

Meanwhile, by making the glass substrate 2 contain Fe, in terms ofFe₂O₃, in an amount of 0.05% or larger according to need, theultraviolet-shielding ability thereof can be enhanced. The content of Feis more preferably 0.07% or higher, even more preferably 0.1% or higher.The enhanced ultraviolet-shielding ability of the glass substrate 2makes the glass substrate 2 capable of functioning as a protectivematerial in the case of using a resin member which is deteriorated byultraviolet light.

From the standpoint of further improving the low-dielectric-losscharacteristics of the glass substrate 2, it is preferable that theglass substrate 2 has a β-OH value in the range of 0.05-0.6 mm⁻¹. β-OHis a value used as an index to the water content of the glass, and isdetermined by examining a glass sample for the absorbance of lighthaving a wavelength of 2.75-2.95 μm and dividing the maximum valuethereof β_(max) by the thickness (mm) of the sample. By regulating theβ-OH value of the glass substrate 2 to 0.6 mm⁻¹ or less, thelow-dielectric-loss characteristics of the glass substrate 2 can befurther improved. The β-OH value of the glass substrate 2 is morepreferably 0.5 mm⁻¹ or less, even more preferably 0.4 mm⁻¹ or less.Meanwhile, in cases when the β-OH value of the glass substrate 2 is 0.05mm⁻¹ or larger, there is no need of performing melting in an extremelydry atmosphere or excessively reducing the water content of the rawmaterials and it is possible to heighten the glass production efficiencyand enhance bubble-free quality etc. of the glass. The β-OH value of theglass substrate 2 is more preferably 0.1 mm⁻¹ or larger, even morepreferably 0.2 mm⁻¹ or larger.

The glass substrate 2 has a thermal expansion coefficient suitable forelectronic devices, depending on, for example, the contents of alkalimetal oxides and alkaline earth metal oxides. Specifically, the averagethermal expansion coefficient thereof over the range of from 50° C. to350° C. is in the range of 3-15 ppm/° C. In cases when the glasssubstrate 2 having such a thermal expansion coefficient is used inconfiguring, for example, a semiconductor package as a high-frequencydevice, it is possible to more properly regulate the difference inthermal expansion coefficient between this glass substrate 2 and othermembers. For example, the difference in thermal expansion coefficientbetween this glass substrate 2 and other members, e.g., semiconductorchips, can be more properly regulated in configuring a through-glass viasubstrate (TGV substrate) of the 2.5-D or 3-D (three dimensional)mounting type for high-frequency applications.

Furthermore, the glass substrate 2 preferably has a Young's modulus of40 GPa or higher. In cases when the glass substrate 2 having such aYoung's modulus is caused to run in steps (wafer process) for producinga high-frequency device, the deflection amount can be reduced to, forexample, 1 mm or less, making it possible to inhibit the occurrence ofhigh-frequency device production failures, etc. The Young's modulus ofthe glass substrate 2 is more preferably 50 GPa or higher, even morepreferably 55 GPa or higher. The glass substrate 2 preferably has aporosity of 0.1% or less. Due to this, high-frequency devices producedusing the glass substrate 2 can be inhibited from making noises, etc.The porosity of the glass substrate 2 is more preferably 0.01% or less,even more preferably 0.001% or less.

The glass substrate 2 preferably has a transmittance at 350-nmwavelength of 50% or higher. The glass substrate 2 having suchtransmittance makes it possible to use an ultraviolet-curing materialin, for example, stacking steps in high-frequency device productionsteps, thereby heightening the efficiency of producing high-frequencydevices. From the standpoint of shortening the period of irradiating theultraviolet-curing material with ultraviolet light in a deviceproduction step and reducing the thickness-direction unevenness in thecuring of the ultraviolet-curing material, it is more preferable thatthe transmittance at 350-nm wavelength of the glass substrate 2 is 70%or higher.

For the same reason, the transmittance at 300-nm wavelength of the glasssubstrate 2 is preferably 50% or higher, more preferably 60% or higher,even more preferably 70% or higher. The transmittance at 250-nmwavelength of the glass substrate 2 is preferably 5% or higher, morepreferably 10% or higher, even more preferably 20% or higher.

The transmittance at 350-nm wavelength of the glass substrate 2 ispreferably 80% or less. Thus, the glass substrate 2 can be made to haveultraviolet-shielding ability and to function as a protective materialfor the case where a resin which is deteriorated by ultraviolet light isused as a member. The transmittance at 350-nm wavelength of the glasssubstrate 2 is more preferably 60% or less, even more preferably 30% orless, most preferably 10% or less.

For the same reason, the transmittance at 300-nm wavelength of the glasssubstrate 2 is preferably 80% or less, more preferably 60% or less, evenmore preferably 30% or less, most preferably 10% or less. Thetransmittance at 250-nm wavelength of the glass substrate 2 ispreferably 60% or less, more preferably 30% or less, even morepreferably 10% or less, most preferably 5% or less.

The glass substrate 2 is not particularly limited in the shape thereof.However, the thickness thereof is preferably in the range of 0.05-1 mm,and each main surface of the glass substrate 2 preferably has an area of225-10,000 cm². In cases when the thickness of the glass substrate 2 is1 mm or less, it is possible to attain thickness and size reductions inhigh-frequency devices, an improvement in the efficiency of producinghigh-frequency devices, etc. Furthermore, the glass substrate 2 can havea heightened ultraviolet transmittance, making it possible to heightenthe efficiency of device production by using an ultraviolet-curingmaterial in device production steps. The thickness of the glasssubstrate 2 is more preferably 0.5 mm or less. Meanwhile, in cases whenthe thickness of the glass substrate 2 is 0.05 mm or larger, this glasssubstrate 2 can retain the strength, etc. when caused to run. Inaddition, this glass substrate 2 can have enhanced ultraviolet-shieldingability and can protect resins which are deteriorated by ultravioletlight. The thickness of the glass substrate 2 is more preferably 0.1 mmor larger, even more preferably larger than 0.2 mm. Moreover, a glasssubstrate 2 according to an embodiment can be provided in a substratesize which includes the thickness shown above and an area of 10,000 cm².It is hence possible to cope with a panel size increase, etc. The areaof the glass substrate 2 is more preferably 3,600 cm² or less.

The glass substrate 2 preferably has a devitrification temperature of1,400° C. or lower. In cases when the devitrification temperaturethereof is 1,400° C. or lower, glass forming can be conducted using aforming apparatus in which the members have lowered set temperatures andcan have a prolonged life. The devitrification temperature thereof ismore preferably 1,350° C. or lower, even more preferably 1,330° C. orlower, especially preferably 1,300° C. or lower. The devitrificationtemperature of a glass is determined in the following manner. Crushedparticles of the glass are placed on a platinum dish and heat-treatedfor 17 hours in an electric furnace controlled so as to have a constanttemperature. The heat-treated sample is examined with an opticalmicroscope to determine both a highest temperature at which crystalprecipitation has occurred in the surface and inside of the glass and alowest temperature at which crystal precipitation has occurred inneither the glass surface nor the inside thereof. The highest and lowesttemperatures are averaged, and the average value is taken as thedevitrification temperature.

Next, a process for producing a glass substrate according to anembodiment is explained. In the case of producing the glass substrateaccording to an embodiment, the glass substrate is produced through: amelting step in which raw glass materials are heated to obtain a moltenglass; a refining step in which bubbles are removed from the moltenglass; a forming step in which the molten glass is formed into a sheetshape to obtain a glass ribbon; and an annealing step in which the glassribbon is gradually cooled to a room-temperature state. Alternatively,use may be made of a method in which the molten glass is formed into ablock, annealed, and then subjected to cutting and polishing to producethe glass substrate.

In the melting step, raw materials are prepared so as to result in adesired composition of the glass substrate, and the raw materials arecontinuously introduced into a melting furnace and heated to preferablyabout 1,450-1,750° C. to obtain a molten glass.

As the raw materials, use can be made of oxides, carbonates, nitrates,hydroxides, halides such as chlorides, and the like. In cases when theprocess includes a step in which the molten glass comes into contactwith platinum as in the melting or refining step, fine platinumparticles may come into the molten glass and be included as foreignmatter in the glass substrate obtained. Use of nitrates as raw materialshas the effect of preventing the inclusion of platinum as foreignmatter.

Usable as the nitrates are strontium nitrate, barium nitrate, magnesiumnitrate, calcium nitrate, and the like. More preferred is to usestrontium nitrate. With respect to the particle size of the rawmaterials, use may be suitably made of raw materials ranging from rawmaterials having such a large particle diameter of several hundredmicrometers that the particles do not remain unmelted to raw materialshaving such a small particle diameter of several micrometers that theparticles neither fly off during raw-material conveyance nor aggregateinto secondary particles. Use of granules is possible. The water contentof the raw materials can be suitably regulated in order to prevent theraw materials from flying off. Melting conditions including β-OH and thedegree of oxidation/reduction of Fe (redox [Fe²⁺/(Fe²⁺+Fe³⁺)]) can alsobe suitably regulated.

The subsequent refining step is a step in which bubbles are removed fromthe molten glass obtained in the melting step. In the refining step, amethod of degassing under reduced pressure may be used, or degassing maybe conducted by heating the molten glass to a temperature higher thanthe temperature used for melting the raw materials. In a step forproducing a glass substrate according to an embodiment, SO₃ or SnO₂ canbe used as a refining agent. Preferred SO₃ sources are the sulfates ofat least one element selected from among Al, Na, K, Mg, Ca, Sr, and Ba.More preferred are the sulfates of the alkaline earth metals. Preferredof these are CaSO₄.2H₂O, SrSO₄, and BaSO₄, because these sulfates arehighly effective in enlarging bubbles.

As a refining agent for the method for degassing performed under reducedpressure, it is preferred to use a halogen such as Cl or F. Preferred Clsources are the chlorides of at least one element selected from amongAl, Mg, Ca, Sr, and Ba. More preferred are the chlorides of the alkalineearth metals. Especially preferred of these are SrCl₂.6H₂O andBaCl₂.2H₂O, because these chlorides are highly effective in enlargingbubbles and have low deliquescence. Preferred F sources are thefluorides of at least one element selected from among Al, Na, K, Mg, Ca,Sr, and Ba. More preferred are the fluorides of the alkaline earthmetals. Even more preferred of these is CaF₂, because this fluoride ishighly effective in enhancing the meltability of raw glass materials.

Tin compounds represented by SnO₂ evolve O₂ gas in molten glasses. Inmolten glasses, SnO₂ at a temperature of 1,450° C. or higher has thefunction of being reduced to SnO to evolve O₂ gas, thereby enlarging thebubbles. In producing the glass substrate 2 according to an embodiment,the raw glass materials are melted by heating to about 1,450-1,750° C.and, hence, the bubbles in the molten glass are more effectivelyenlarged. In the case of using SnO₂ as a refining agent, the rawmaterials are prepared so that tin compounds are contained in an amountof 0.01% or larger in terms of SnO₂ based on the whole glass matrixcomposition, which is taken as 100%. In cases when the content of SnO₂is 0.01% or higher, the refining function is obtained in melting the rawglass materials. The content thereof is preferably 0.05% or higher, morepreferably 0.10% or higher. In cases when the content of SnO₂ is 0.3% orless, the glass is inhibited from being colored or devitrified. Thecontent of tin compounds in the alkali-free glass is more preferably0.25% or less, even more preferably 0.2% or less, especially preferably0.15% or less, in terms of SnO₂ based on the whole glass matrixcomposition, which is taken as 100%.

The subsequent forming step is a step in which the molten glass fromwhich bubbles have been removed in the refining step is formed into asheet shape to obtain a glass ribbon. In the forming step, a knowntechnique for forming a glass into a sheet shape can be used, such as,for example, the float process, in which a molten glass is poured onto amolten metal, e.g., tin, to obtain a sheet-shaped glass ribbon, anoverflow downdraw process (fusion process) in which a molten glass iscaused to flow downward from a trough member, or a slit downdraw processin which a molten glass is caused to flow down through a slit.

Next, the annealing step is a step in which the glass ribbon obtained inthe forming step is cooled to a room-temperature state under controlledcooling conditions. In the annealing step, the glass ribbon is cooledfrom the annealing point to the strain point at an average cooling rateof R and then further cooled gradually to a room-temperature state undergiven conditions. The annealed glass ribbon is cut to obtain a glasssubstrate.

In case where the cooling rate R in the annealing step is too high, thecooled glass is prone to have a residual strain. In addition, theequivalent cooling rate, which is a parameter that reflects a fictivetemperature, becomes too high, making it impossible to obtainlow-dielectric-loss characteristics. It is hence preferred to set the Rso as to result in an equivalent cooling rate of 800° C./min or less.The equivalent cooling rate is more preferably 400° C./min or less, evenmore preferably 100° C./min or less, especially preferably 50° C./min orless. Meanwhile, in case where the cooling rate is too low, there is aproblem in that the step requires too long a time period, resulting in adecrease in production efficiency. It is hence preferred to set thecooling rate at 0.1° C./min or higher. The cooling rate is morepreferably 0.5° C./min or higher, even more preferably 1° C./min orhigher.

A definition of the equivalent cooling rate and a method for evaluationthereof are as follows. A glass having a composition to be examined andhaving been processed into a rectangular parallelepiped of 10 mm×10mm×0.3-2.0 mm is held at [strain point+170° C.] for 5 minutes using aninfrared-heating electric furnace and then cooled to room temperature(25° C.). This operation is conducted to produce a plurality of glasssamples by performing the cooling at various cooling rates ranging from1 to 1,000° C./min.

A precision refractometer (e.g., KPR2000, manufactured by ShimadzuDevice Corp.) is used to measure the refractive index n_(d) for d-line(wavelength, 587.6 nm) of each of the plurality of glass samples. Forthe measurement, use may be made of a V-block method or a minimumdeviation method. The obtained values of n_(d) are plotted against thelogarithm of the cooling rates, thereby obtaining a calibration curveregarding a relationship between n_(d) and cooling rate.

Next, a glass having the same composition and actually produced throughthe steps of melting, forming, cooling, etc. is examined for n_(d) bythe measuring method shown above. A cooling rate corresponding to then_(d) obtained (the cooling rate being referred to as equivalent coolingrate in this embodiment) is determined from the calibration curve.

The present invention is not limited to the embodiments described above.Modifications, improvements, and the like made within the range wherethe objects of the present invention can be achieved are included in thepresent invention. For example, in the case of producing a glasssubstrate according to the present invention, a plate-shaped glass maybe obtained by press forming, in which a molten glass is directly formedinto a plate shape.

Furthermore, for producing a glass substrate according to the presentinvention, a crucible made of platinum or of an alloy including platinumas a main component (hereinafter referred to as a platinum crucible) maybe used as a melting vessel or a refining vessel, besides the productionprocess in which a melting vessel made of a refractory is used. In thecase of using a platinum crucible, a melting step may be performed inthe following manner. Raw materials are prepared so as to result in thecomposition of the glass substrate to be obtained, and the platinumcrucible containing the raw materials is heated in an electric furnaceto preferably about 1,450-1,700° C. A platinum stirrer is insertedthereinto to stir the contents for 1-3 hours, thereby obtaining a moltenglass.

In a forming step among steps for glass substrate production with theplatinum crucible, the molten glass is poured out, for example, onto acarbon plate or into a casting mold to form the molten glass into aplate or block shape. In an annealing step, the formed glass is held ata temperature of typically about Tg+50° C., subsequently cooled toaround the strain point at a rate of about 1-10° C./min, and then cooledto a room-temperature state at such a cooling rate that no strainremains. The cooled glass is cut into a given shape and polished toobtain a glass substrate. The glass substrate obtained by the cuttingmay be heated, for example, to a temperature of about Tg+50° C. and thengradually cooled to a room-temperature state at a given cooling rate.Thus, the equivalent cooling temperature of the glass can be regulated.

The circuit board 1 employing the above-described glass substrate 2according to an embodiment is suitable for use in high-frequency devicesin which high-frequency signals, in particular, high-frequency signalshaving a frequency exceeding 30 GHz and even high-frequency signals of35 GHz or higher, are processed. This circuit board 1 can reduce thetransmission loss of such high-frequency signals to improve the quality,intensity, and other properties of the high-frequency signals. The glasssubstrate 2 and the circuit board 1 according to an embodiment aresuitable for high-frequency devices (electronic devices) such assemiconductor devices for use in communication appliances, such as, forexample, cell phones, smartphones, personal digital assistants, andWi-Fi appliances, and for surface acoustic wave (SAW) devices, radarcomponents such as radar transceivers, antenna components such asliquid-crystal antennas, etc.

EXAMPLES

The present invention is explained below in detail by reference toExamples, but the present invention is not limited to the followingExamples. Examples 1 to 3 and 7 to 25 are working examples according tothe present invention, and Examples 4 to 6 are comparative examples.

Examples 1 to 3 and 7 to 25

Glass substrates respectively having the compositions shown in Tables 1to 4 and each having a thickness of 0.125 mm, a shape of 50 mm×50 mm,and an arithmetic average roughness Ra of the main surfaces of 1.0 nmwere prepared. Each glass substrate was produced by a melting methodusing a platinum crucible. Raw materials including silica sand weremixed so as to result in 1 kg in terms of glass weight, therebyproducing a batch. A sulfate was added thereto in an amount of 0.1-1% interms of SO₃ and in terms of mole percent on the basis of oxides, and0.16% F and 1% Cl were further added, the amount of the raw materialshaving the desired composition being taken as 100%. The raw materialswere placed in a platinum crucible and melted by heating at atemperature of 1,650° C. in an electric furnace for 3 hours, therebyobtaining a molten glass. In the melting, a platinum stirrer wasintroduced into the platinum crucible and the contents were stirred for1 hour to homogenize the glass. The molten glass was poured out onto acarbon plate and formed into a plate shape. Thereafter, the plate-shapedglass was introduced into an electric furnace having a temperature ofabout Tg+50° C. and held therein for 1 hour. Subsequently, the electricfurnace was cooled to Tg−100° C. at a cooling rate of 1° C./min and thenallowed to cool until the glass cooled to room temperature. Thereafter,the glass was cut and polished into a plate shape.

The glass substrates of Examples 1 to 3 and 7 to 25 were examined forthe average thermal expansion coefficient over the range of from 50° C.to 350° C., β-OH value, Young's modulus, porosity, transmittance at awavelength of 350 nm, density, specific modulus, and devitrificationtemperature, and these properties are shown in Tables 5 to 8. Thenumerals given in parentheses in the tables are ones determined bycalculations. In Tables 9 to 12 are shown the dielectric dissipationfactor at 35 GHz, relative permittivity at 35 GHz, wiring line width,transmission loss at 35 GHz, and transmission loss at 110 GHz. Asillustrated in FIG. 1, a copper wiring layer having a thickness of 0.125mm was formed as signal wiring on a first main surface of the glasssubstrate, and a copper layer having a thickness of 0.125 mm was formedas solid-film ground wiring on a second main surface. The circuit boardthus produced was subjected to the property evaluation which will bedescribed later.

Example 4

A soda-lime glass substrate produced by the float process was prepared,the glass substrate having the composition shown in Table 1 and having athickness of 0.125 mm, a shape of 50 mm×50 mm, and an arithmetic averageroughness Ra of the main surfaces of 1.0 nm. The properties of the glasssubstrate of Example 4 are shown in Tables 5 and 9 like those ofExample 1. A copper wiring layer having a thickness of 0.125 mm and acopper layer having a thickness of 0.125 mm were formed on both mainsurfaces of the glass substrate as in Example 1, and the resultantcircuit board was subjected to the property evaluation which will bedescribed later.

Example 5

An alkali-free glass substrate produced by the float process wasprepared, the glass substrate having the composition shown in Table 1and having a thickness of 0.125 mm, a shape of 50 mm×50 mm, and anarithmetic average roughness Ra of the main surfaces of 1.0 nm. Theproperties of the glass substrate of Example 5 are shown in Tables 5 and9 like those of Example 1. A copper wiring layer having a thickness of0.125 mm and a copper layer having a thickness of 0.125 mm were formedon both main surfaces of the glass substrate as in Example 1, and theresultant circuit board was subjected to the property evaluation whichwill be described later.

Example 6

A quartz glass substrate produced by a vapor-phase synthesis method wasprepared, the glass substrate having the composition shown in Table 1and having a thickness of 0.125 mm, a shape of 50 mm×50 mm, and anarithmetic average roughness Ra of the main surfaces of 1.0 nm. In thecomposition shown in Table 1, “0” indicates that the content of thecomponent is less than 0.05%. The properties of the glass substrate ofExample 6 are shown in Tables 5 and 9 like those of Example 1. A copperwiring layer having a thickness of 0.125 mm and a copper layer having athickness of 0.125 mm were formed on both main surfaces of the glasssubstrate as in Example 1, and the resultant circuit board was subjectedto the property evaluation which will be described below.

Methods for determining the properties are shown below.

(Relative Permittivity, Dielectric Dissipation Factor)

A cavity resonator and a vector network analyzer were used to make ameasurement in accordance with the method as provided for in JIS R1641(year 2007). The measuring frequency was 35 GHz, which was the airresonance frequency for the cavity resonator.

(Average Thermal Expansion Coefficient)

A differential thermodilatometer was used to make a measurement inaccordance with the method as provided for in JIS R3102 (year 1995). Themeasurement was made over a temperature range of 50-350° C. The unit isppm/° C.

(Young's Modulus)

A glass having a thickness of 0.5-10 mm was examined for Young's modulusby an ultrasonic pulse method in accordance with the method as providedfor in JIS Z 2280. The unit is GPa.

(Transmittance)

A visible and ultraviolet spectrophotometer was used to measure thetransmittance of a mirror-polished glass having a given thickness. Thetransmittance was shown in terms of external transmittance including aloss due to reflection.

(Porosity)

A glass substrate was examined for bubbles contained therein with anoptical microscope to determine the number of the bubbles and thediameters thereof. The volume of bubbles contained per unit volume wascalculated to thereby determine the porosity.

(β-OH)

β-OH was determined by the method described hereinabove with regard toan embodiment.

(Ra)

The average roughness of a 10-μm-square region in a glass surface wasdetermined with an AFM in accordance with the method as provided for inJIS B0601 (year 2001).

(Density)

Glass masses weighing about 20 g and containing no bubbles were examinedfor density by Archimedes' method.

(Devitrification Temperature)

Crushed particles of a glass were placed on a platinum dish andheat-treated for 17 hours in an electric furnace controlled so as tohave a constant temperature. The heat-treated sample was examined withan optical microscope, and the highest temperature at which crystalprecipitation occurred in the inside of the glass and the lowesttemperature at which no crystal precipitation occurred in the inside ofthe glass were averaged. The average value was taken as thedevitrification temperature.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Composition SiO₂ 68.0 69.5 71.0 71.1 66.1 100 [mol %] Al₂O₃ 4.0 5.5 4.01.1 11.3 0 B₂O₃ 21.0 15.0 21.3 0 7.8 0 Al₂O₃ + B₂O₃ 25.0 20.5 25.3 1.119.1 0 MgO 0 3.0 0 6.9 5.1 0 CaO 1.0 4.0 0 8.3 4.5 0 SrO 6.0 3.0 3.8 05.2 0 BaO 0 0 0 0 0 0 Total content RO*1 7.0 10.0 3.8 15.2 14.8 0 Na₂O0.009 0.007 0.012 12.4 0.07 0 K₂O 0.003 0.004 0.006 0.2 0.01 0 Totalcontent R₂O*2 0.012 0.011 0.018 12.6 0.08 0 Fe₂O₃ 0.002 0.001 0.003 0.040.003 0 Proportion Al₂O₃/(Al₂O₃ + B₂O₃) 0.16 0.27 0.16 1 0.59 —Na₂O/(Na₂O + K₂O) 0.75 0.64 0.67 0.98 0.88 — *1Total content of alkalineearth metal oxides. *2Total content of alkali metal oxides.

TABLE 2 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12Composition SiO₂ 62.0 60.0 60.0 58.0 62.0 58.0 [mol %] Al₂O₃ 10.0 10.010.0 10.0 8.0 10.0 B₂O₃ 21.0 23.0 26.0 26.0 23.0 25.0 Al₂O₃ + B₂O₃ 31.033.0 36.0 36.0 31.0 35.0 MgO 2.0 2.0 1.0 3.0 2.0 2.0 CaO 3.0 3.0 2.0 2.03.0 3.0 SrO 2.0 2.0 1.0 1.0 2.0 2.0 BaO 0 0 0 0 0 0 Total content RO*17.0 7.0 4.0 6.0 7.0 7.0 Na₂O 0.010 0.015 0.008 0.003 0.005 0.005 K₂O0.003 0.003 0.005 0.001 0.001 0.001 Total content R₂O*2 0.013 0.0180.013 0.004 0.006 0.006 Fe₂O₃ 0.008 0.007 0.006 0.007 0.008 0.009Proportion Al₂O₃/(Al₂O₃ + B₂O₃) 0.32 0.30 0.28 0.28 0.26 0.29Na₂O/(Na₂O + K₂O) 0.77 0.83 0.62 0.75 0.83 0.83 *1Total content ofalkaline earth metal oxides. *2Total content of alkali metal oxides.

TABLE 3 Example 13 Example 14 Example 15 Example 16 Example 17 Example18 Composition SiO₂ 60.0 60.0 60.0 60.0 60.0 60.0 [mol %] Al₂O₃ 8.0 10.05.0 2.0 0 0 B₂O₃ 25.0 23.0 28.0 31.0 33.0 36.0 Al₂O₃ + B₂O₃ 33.0 33.033.0 33.0 33.0 36.0 MgO 2.0 4.0 2.0 2.0 2.0 1.0 CaO 3.0 2.0 3.0 3.0 3.02.0 SrO 2.0 1.0 2.0 2.0 2.0 1.0 BaO 0 0 0 0 0 0 Total content RO*1 7.07.0 7.0 7.0 7.0 4.0 Na₂O 0.005 0.005 0.005 0.005 0.005 0.005 K₂O 0.0010.001 0.001 0.001 0.001 0.001 Total content R₂O*2 0.006 0.006 0.0060.006 0.006 0.006 Fe₂O₃ 0.008 0.010 0.006 0.006 0.005 0.005 ProportionAl₂O₃/(Al₂O₃ + B₂O₃) 0.24 0.30 0.15 0.06 0 0 Na₂O/(Na₂O + K₂O) 0.83 0.830.83 0.83 0.83 0.83 *1Total content of alkaline earth metal oxides.*2Total content of alkali metal oxides.

TABLE 4 Example 19 Example 20 Example 21 Example 22 Example 23 Example24 Example 25 Composition SiO₂ 60.0 63.0 62.0 64.0 65.0 62.0 64.0 [mol%] Al₂O₃ 10.0 8.0 8.0 9.0 10.0 7.2 8.5 B₂O₃ 21.0 16.0 23.0 18.5 14.023.0 18.5 Al₂O₃ + B₂O₃ 31.0 24.0 31.0 27.5 24.0 30.2 27.0 MgO 2.0 4.04.0 2.5 4.0 4.3 2.5 CaO 3.0 5.0 2.0 3.5 5.0 2.5 4.0 SrO 4.0 3.0 1.0 2.52.0 1.0 2.5 BaO 0 1.0 0.0 0.0 0.0 0.0 0.0 Total content RO*1 9.0 13.07.0 8.5 11.0 7.8 9.0 Na₂O 0.01 0.012 0.004 0.006 0.005 0.005 0.008 K₂O0.002 0.003 0.001 0.001 0.001 0.001 0.002 Total content R₂O*2 0.0120.015 0.005 0.007 0.006 0.006 0.010 Fe₂O₃ 0.008 0.010 0.010 0.003 0.0020.005 0.005 Proportion Al₂O₃/Al₂O₃+ B₂O₃ 0.32 0.33 0.26 0.33 0.42 0.240.31 Na₂O/Na₂O + K₂O 0.83 0.80 0.80 0.86 0.83 0.83 0.80 *1Total contentof alkaline earth metal oxides. *2Total content of alkali metal oxides.

TABLE 5 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Average thermal expansion 3.4 3.3   (2.8) 8.5 3.8 0.7 coefficient [ppm/°C.] β-OH [mm⁻¹] 0.21 0.34 — 0.19 0.28 — Young's modulus [GPa] 58 66 (51)73 76 74 Porosity [%] 0 0  0 0 0 0 Transmittance [%] (0.3-0.4 mmt) 90 9090 90 90 93 Density [g/cm³] 2.32 2.34    (2.24) 2.49 2.50 2.20 Specificmodulus [GPa · cm³/g] 25 28 23 29 30 34 Devitrification temperature [°C.] ≤1200° C. ≤1200° C. ≤1200° C. ≤1000° C. 1270 —

TABLE 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12Average thermal expansion (3.0) (3.1) (2.7) (2.9) (3.1) (3.1)coefficient [ppm/° C.] β-OH [mm⁻¹] (0.35) (0.35) (0.35) (0.35) 0.43(0.35) Young's modulus [GPa] 62 61 58 59 58 59 Porosity [%] 0 0 0 0 0 0Transmittance [%] (0.3-0.4 mmt) 90 90 90 90 90 90 Density [g/cm³] 2.302.30 2.25 2.26 2.27 2.29 Specific modulus [GPa · cm³/g] 27 27 26 26 2626 Devitrification temperature [° C.] 1330 1295 ≥1420° C. ≥1420° C. 11701310

TABLE 7 Example 13 Example 14 Example 15 Example 16 Example 17 Example18 Average thermal expansion (3.1) (2.9) (3.2) (3.3)  (3.4)  (3.0) coefficient [ppm/° C.] β-OH [mm⁻¹] 0.48 (0.35) 0.52 (0.35) (0.35) (0.35)Young's modulus [GPa] 57 61 53 (42)    (39)    (35)    Porosity [%] 0 00 0   0   0   Transmittance [%] (0.3-0.4 mmt) 90 90 90 — — — Density[g/cm³] 2.27 2.28 2.23 (2.20) (2.17) (2.11) Specific modulus [GPa ·cm³/g] 25 27 24 19    18    16    Devitrification temperature [° C.]1160 1340 1040 — — —

TABLE 8 Example 19 Example 20 Example 21 Example 22 Example 23 Example24 Example 25 Average thermal expansion   (3.4)   (3.8)   3.1   3.4  (3.4) 3.5 3.5 coefficient [ppm/° C.] β-OH [mm⁻¹]    (0.35)    (0.35)   (0.35)    (0.35)    (0.35) 0.49 0.53 Young's modulus[GPa] (59) (64)(59) (64) (70) 59 64 Porosity [%]  0  0  0  0  0 0 0 Transmittance [%](0.3-0.4 mmt) 90 90 90 90 90 90 90 Density [g/cm³]    (2.36)    (2.42)   (2.26)    (2.33)    (2.38) (2.26) (2.33) Specific modulus [GPa ·cm³/g] 25 26 26 27 29 26 27 Devitrification temperature [° C.] — — 1230 1220  1300  1230 1300

(Transmission Loss Calculation Example)

In order to ascertain the influence of the dielectric properties of theglass substrate materials of Examples 1 to 6 on the transmission loss ofhigh-frequency signals, a transmission loss in a transmission line wascalculated using a simplified model. As an analysis method, use was madeof commercial moment-method simulator Sonnet Lite® (manufactured bySonnet Software Inc.). The transmission line was a microstrip line(MSL). The analysis model was as follows. The copper wiring layer formedon one of the main surfaces of the glass substrate was made to have awidth (shown in Tables 9 to 12) which resulted in a characteristicimpedance for the line of 50Ω, and S parameters (scattering parametersS21) at 1-110 GHz were calculated. The surface roughness of the copperlayer was set at such a value that the surface was so smooth that theskin effect was not problematic. The calculated values of S21(transmission characteristics) are shown in FIG. 2. The values of signaltransmission loss at 35 GHz and 110 GHz were shown in Tables 9 to 12.

TABLE 9 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Relative permittivity 4.39 4.57 4.09 7.13 5.41 3.87 @ 35 GHz Dielectricdissipation factor @ 35 2.48 3.04 1.82 20.9 8.98 0.146 GHz (×10⁻³)Wiring line width [mm] 0.237 0.23 0.25 0.146 0.185 0.26 Transmissionloss 0.39 0.44 0.35 1.83 0.88 0.26 @ 35 GHz [dB/cm] Transmission loss1.11 1.20 0.96 5.84 2.76 0.66 @ 110 GHz [dB/cm]

TABLE 10 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12Relative permittivity 4.59 4.58 4.39 4.43 4.43 4.55 @ 35 GHz Dielectricdissipation factor @ 35 3.27 3.25 2.32 2.74 2.86 3.38 GHz (×10⁻³) Wiringline width [mm] 0.23 0.23 0.237 0.235 0.235 0.231 Transmission loss 0.450.45 0.39 0.41 0.42 0.45 @ 35 GHz [dB/cm] Transmission loss 1.26 1.261.07 1.16 1.18 1.28 @ 110 GHz [dB/cm]

TABLE 11 Example 13 Example 14 Example 15 Example 16 Example 17 Example18 Relative permittivity 4.46 4.51 4.26 4.10 3.84 3.79 @ 35 GHzDielectric dissipation factor 2.76 2.98 2.39 1.94 1.85 2.01 @ 35 GHz(×10⁻³) Wiring line width [mm] 0.234 0.232 0.242 0.25 0.26 0.264Transmission loss 0.41 0.43 0.38 0.35 0.33 0.34 @ 35 GHz [dB/cm]Transmission loss 1.16 1.21 1.08 0.98 0.96 0.97 @ 110 GHz [dB/cm]

TABLE 12 Example 19 Example 20 Example 21 Example 22 Example 23 Example24 Example 25 Relative permittivity (4.85) (5.12) 4.34 4.63 4.84 4.364.61 @ 35 GHz Dielectric dissipation factor (4.23) (5.44) 2.64 3.40 4.802.63 3.56 @ 35 GHz (×10⁻³) Wiring line width [mm] 0.22 0.21 0.24 0.2280.22 0.24 0.228 Transmission loss 0.52 0.60 0.40 0.46 0.55 0.41 0.47 @35 GHz [dB/cm] Transmission loss 1.48 1.76 1.12 1.29 1.58 1.10 1.32 @110 GHz [dB/cm]

As shown in FIG. 2 and Tables 9 to 12, the circuit boards employing theglass substrates of Examples 1 to 3 and 7 to 25 can have improvedtransmission characteristics in the high-frequency range as comparedwith the circuit boards employing the conventional soda-lime glasssubstrate of Example 4 and the conventional alkali-free glass substrateof Example 5, and can attain low-transmission-loss characteristics inthe high-frequency range which are close to those of the circuit boardemploying the conventional quartz glass substrate of Example 6. Thequartz glass substrate of Example 6 has a thermal expansion coefficientas low as 0.7 ppm/° C. and, hence, when this glass substrate is used forconfiguring an electronic device, there is an increased difference inthermal expansion coefficient between this glass substrate and othermembers. A practical electronic device cannot hence be providedtherewith. As shown in Example 5, the conventional alkali-free glasssubstrate, although alkali-free, contains an alkali component in anamount of about 0.05-0.1%.

The glass of Example 21, as an Example for examining ultraviolettransmittance, was modified by changing the content of Fe₂O₃, and platesthereof having a thickness of 0.5 mm or 1.0 mm were examined fortransmittance at wavelengths of 250, 300, and 350 nm. The results of theexamination are shown in Table 13. The transmittance was measured with avisible and ultraviolet spectrophotometer. It can be seen from theresults that the ultraviolet transmittance of a glass can be regulatedto a desired value by regulating the thickness of the glass plate andthe Fe₂O₃ content thereof.

TABLE 13 Example 21 Fe₂O₃ [wt %] 0.01 0.05 0.1 0.01 0.05 0.1 Platethickness [mm] 1.0 1.0 1.0 0.5 0.5 0.5 Transmittance [%] @ 250 nm 12 3 131 17 11 Transmittance [%] @ 300 nm 82 62 43 86 75 62 Transmittance [%]@ 350 nm 90 87 83 91 89 87

INDUSTRIAL APPLICABILITY

The glass substrates for a high-frequency device of the presentinvention have excellent low-dielectric-loss characteristics forhigh-frequency signals. The circuit board employing the glass substratehaving such properties has excellent low-transmission-losscharacteristics for high-frequency signals. The glass substrate and thecircuit board, which have such properties, are useful in allhigh-frequency electronic devices in which high-frequency signals havinga frequency exceeding 10 GHz, in particular, high-frequency signalshaving a frequency exceeding 30 GHz and even high-frequency signals of35 GHz or higher, are processed. For example, the glass substrate andthe circuit board are useful in applications such as the glasssubstrates of communication appliances, frequency filter components suchas SAW devices and FBARs, band pass filters such as waveguides, SIW(substrate integrated waveguide) components, radar components, andantenna components (in particular, liquid-crystal antennas optimal forsatellite communication).

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

1 . . . circuit board; 2 . . . glass substrate; 2 a, 2 b . . . mainsurfaces; 3, 4 . . . wiring layers.

1. A glass substrate for a high-frequency device, which comprises SiO₂as a main component, the glass substrate having a total content ofalkali metal oxides in the range of 0.001-5% in terms of mole percent onthe basis of oxides, the alkali metal oxides having a molar ratiorepresented by Na₂O/(Na₂O+K₂O) in the range of 0.01-0.99, and the glasssubstrate having a total content of Al₂O₃ and B₂O₃ in the range of 1-40%in terms of mole percent on the basis of oxides and having a molar ratiorepresented by Al₂O₃/(Al₂O₃+B₂O₃) in the range of 0-0.45, wherein atleast one main surface of the glass substrate has a surface roughness of1.5 nm or less in terms of arithmetic average roughness Ra, and theglass substrate has a dielectric dissipation factor at 35 GHz of 0.007or less.
 2. A glass substrate for a high-frequency device, whichcomprises SiO₂ as a main component, the glass substrate having a totalcontent of alkali metal oxides in the range of 0.001-5% in terms of molepercent on the basis of oxides, the alkali metal oxides having a molarratio represented by Na₂O/(Na₂O+K₂O) in the range of 0.01-0.99, and theglass substrate having a total content of alkaline earth metal oxides inthe range of 0.1-13% in terms of mole percent on the basis of oxides,wherein at least one main surface of the glass substrate has a surfaceroughness of 1.5 nm or less in terms of arithmetic average roughness Ra,and the glass substrate has a dielectric dissipation factor at 35 GHz of0.007 or less.
 3. The glass substrate for a high-frequency deviceaccording to claim 2, which has a total content of Al₂O₃ and B₂O₃ in therange of 1-40% in terms of mole percent on the basis of oxides and has amolar ratio represented by Al₂O₃/(Al₂O₃+B₂O₃) in the range of 0-0.45. 4.The glass substrate for a high-frequency device according to claim 1,which has a content of B₂O₃ in the range of 9-30% and a content of Al₂O₃in the range of 0-10%, in terms of mole percent on the basis of oxides.5. The glass substrate for a high-frequency device according to claim 1,which has a content of Fe, in terms of Fe₂O₃, of 0.012% or less in termsof mole percent on the basis of oxides.
 6. The glass substrate for ahigh-frequency device according to claim 1, which has β-OH value in therange of 0.05-0.6 mm⁻¹.
 7. The glass substrate for a high-frequencydevice according to claim 1, which has a relative permittivity at 35 GHzof 10 or less.
 8. The glass substrate for a high-frequency deviceaccording to claim 1, which has an average thermal expansion coefficientover the range of from 50° C. to 350° C. in the range of 3-15 ppm/° C.9. The glass substrate for a high-frequency device according to claim 1,which has a Young's modulus of 40 GPa or higher.
 10. The glass substratefor a high-frequency device according to claim 1, which has a porosityof 0.1% or less.
 11. The glass substrate for a high-frequency deviceaccording to claim 1, which has a transmittance at 350-nm wavelength of50% or higher.
 12. The glass substrate for a high-frequency deviceaccording to claim 1, which has a thickness in the range of 0.05-1 mmand a substrate area in the range of 225-10,000 cm².
 13. The glasssubstrate for a high-frequency device according to claim 1, which isamorphous.
 14. A circuit board for a high-frequency device, comprising:the glass substrate according to claim 1; and a wiring layer formed onthe main surface of the glass substrate, wherein the circuit board has atransmission loss at 35 GHz of 1 dB/cm or less.
 15. The glass substratefor a high-frequency device according to claim 2, which has a content ofB₂O₃ in the range of 9-30% and a content of Al₂O₃ in the range of 0-10%,in terms of mole percent on the basis of oxides.
 16. The glass substratefor a high-frequency device according to claim 2, which has a content ofFe, in terms of Fe₂O₃, of 0.012% or less in terms of mole percent on thebasis of oxides.
 17. The glass substrate for a high-frequency deviceaccording to claim 2, which has β-OH value in the range of 0.05-0.6mm⁻¹.
 18. The glass substrate for a high-frequency device according toclaim 2, which has a relative permittivity at 35 GHz of 10 or less. 19.The glass substrate for a high-frequency device according to claim 2,which has an average thermal expansion coefficient over the range offrom 50° C. to 350° C. in the range of 3-15 ppm/° C.
 20. The glasssubstrate for a high-frequency device according to claim 2, which has aYoung's modulus of 40 GPa or higher.
 21. The glass substrate for ahigh-frequency device according to claim 2, which has a porosity of 0.1%or less.
 22. The glass substrate for a high-frequency device accordingto claim 2, which has a transmittance at 350-nm wavelength of 50% orhigher.
 23. The glass substrate for a high-frequency device according toclaim 2, which has a thickness in the range of 0.05-1 mm and a substratearea in the range of 225-10,000 cm².
 24. The glass substrate for ahigh-frequency device according to claim 2, which is amorphous.
 25. Acircuit board for a high-frequency device, comprising: the glasssubstrate according to claim 2; and a wiring layer formed on the mainsurface of the glass substrate, wherein the circuit board has atransmission loss at 35 GHz of 1 dB/cm or less.